Musical tuning instrument utilizing digital techniques

ABSTRACT

A musical tuning instrument for use by high school bands is disclosed. Instrument produces reference tones of the musical scale. Instrument also indicates whether a sounded tone is higher or lower than a particular musical note. Indication is visual. An eight MgHz reference oscillator feeds a programmable counter to produce close approximations to the musical scale. Sounded tones are compared in frequency with the reference frequencies and the comparison indicated by a pattern on a light emitting diode display.

[ Jan. 21, 1975 I MUSICAL TUNING INSTRUMENT UTILIZING DIGITAL TECHNIQUES[76] Inventor: Ranald Otis Whitaker, 4719 Squire Dr., Indianapolis, Ind.46241 22 Filed: May 29,1973

211 Appl. No.: 364,678

[52] US. Cl 84/454, 84/101, 84/444 [51] Int. Cl ..G10g 7/02 [58] Fieldof Search 84/454, 101, 444; 324/79 R, 79 D, 81

[56] References Cited UNITED STATES PATENTS 2,924,776 2/1960 Peterson324/79 D 2,958,250 11/1960 Poehler r I 84/454 3,351,854 ll/I967 Sheen etal. 324/79 R 3,509,454 4/1970 Gossel 84/101 3,696,293 10/1972 Hoffman etal I 324/79 D 3,722,353 3/1973 Westhaver 324/79 R OTHER PUBLICATIONS R.Stapelfeldt, Approximating the Frequencies of the Musical Scale withDigital Counter Circuits," JASA. pages 478-479, Vol. 46.

A. C. Van Der Woerd, New Electronic Tuning Device For Pianos, JASA,pages 2010-2017, Vol. 51.

Primary ExaminerRichard B. Wilkinson Assistant Examiner-U. Weldon [57]ABSTRACT 3 Claims, 2 Drawing Figures l5 4 5 f h FREQUENCY AUDIOSYNTHESIZER AMPLIFIER (I re CRYSTAL OCTAVE PROGRAMMABLE OSCILLATOR 4 8'66 645 HZ q DIVIDERQ DIVIDER l4 2/ 6' f mESET VARIABLE PROCRAMMABLEFREQUENCY DlVlDER OSCILLATOR s STACE (I2 L SENSITIVITYO SELECT DlVlDER 00- CODE BINARY TO 4-STAGE DIVIDER HEXADECIMAL CONVERTER AUDIO 4-STAGESENSITIVITY AMPLIFIER -DIV|DER NABLE PAIENIEIJJIIIIZ I III/b r' wFREQUENCY AUDIO SYNTHESIZER FIG. I AMPLIFIER (I F CRYSTAL OCTAVEPROGRAMMABLE OSCILLATOR 0 8}66 645MHz DIl/IDER DIVIDER 2 MESH VARIABLEPROCRAMMABLE FREQUENCY DIVIDER- OSCILLATOR s sTAcE l I I |2 LsENsITlvITYlgL sELEcT DIVIDER 1 -CODE BINARY TO 4-STAGE DIvIDERHEXADECIMAL v coNvERTE AUDIO I lsENsITlvITYol' AMPLIFIER DIVIDER ENABLEv 4-STAGE 3 F' 2 IO/ 4; 5

, o SENSITIVITY AUDIO 6 DIVIDER if AMPLIFIER MUSICAL TUNING INSTRUMENTUTILIZING DIGITAL TECHNIQUES BACKGROUND OF THE INVENTION Skilledmusicians generally tune their instruments by listening to referencetones and adjusting their pieces to the same frequency. Beats are heardas the tone generated by the instrument approaches the reference tone infrequency. The musician tunes for zero beat. Persons of lesser skill,such as members of high school bands, find it beneficial to useadditional tuning aids. Such aids generally are visual in nature.Typical is the strobo scopic display in which whirling discs form avisual pattern in response to a tone generated by the student. Thepattern moves clockwise or counterclockwise depending upon whether thestudent is tuned high or low. The student adjusts his piece until thepattern assumes a stationary position. The stroboscopic unit suffersseveral shortcomings:

I. It does not give an audible tone to induce the student to tune by earin a professional manner.

2. It is generally too heavy to be carried in suitcase fashion. It isnot easily moved.

3. It is expensive-presently costing some $750.00.

4. It has moving parts and vacuum tubes, both of which contribute toservice requirements SUMMARY OF THE INVENTION A crystal referenceoscillator provides a reference signal which is divided down by aprogrammable divider to produce close approximations of the severalfrequencies of the musical scale. An audio output section generatestones for use by the student. The student may also play his piece into amicrophone which feeds to the instrument. The frequency of the tonegenerated by the student is compared by the instrument with a musicalscale frequency obtained from the programmable divider. As a result ofthe comparison a pattern of light and dark Leds (light emitting diodesappears in a display. The pattern moves clockwise or counterclockwisedepending upon whether the student is tuned high or low. Two additionaldivision circuits permit adjustment of the sensitivity of the display.In the most coarse position the tone generated by the student must shiftapproximately 16 cycles from the reference signal before the displaypattern rotates one revolution. In the fine position a shift of onecycle causes a rotation of one revolution.

Advantages over conventional instruments are:

l. A tone is generated to assist the student in learning to tune by ear.

2. No moving parts are involved. Solid state circuitry is usedthroughout. These two items contribute greatly to reliability ofproduct.

3. Mass and size of the unit is reduced over conventional tuning aids byan order of magnitude.

4. Cost is reduced by a similar order of magnitude.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a block diagram indicatinginterrelationship of the several sections of a musical tuning instrumentbuilt according to the present invention. 7

FIG. 2 is a block diagram indicating an alternate embodiment of thepresent invention. Specifically, FIG. 2 shows an alternate connection ofselected components of FIG. 1.

DETAILS OF THE INVENTION Referring to FIG. I, oscillator l is preferablya crystal unit providing a very stable output frequency of 8,166,645 H2.A Motorola type KlO9lA has been used and is suitable.

While the instrument is capable of providing tuning assistance for eachnote of the musical scale, understanding of the operation of the systemmay best be gained through consideration of a single note. Since middleA having a frequency of 440 Hz is most commonly used for tuning it willbe used in the following explanation.

Octave divider 2 provides seven outputs corresponding to the sevenoctaves of the musical scale. The output selector switch is set to themiddle octave in which A 440 is found. Two TTL 7493 made by TexasInstruments Corporation integrated circuits are suitable for thisdivider.

Programmable divider 3 consisting of 12 binary stages is programmed in12 ways to provide close approximations of the 12 notes of the octave.In the present case it is programmed to provide at its output a signalwhose frequency closely approximates the A 440. Several programmingtechniques are common in the art. They will not be discussed. Thedivider may consist of three TTL type 8281A made by NationalSemiconductor Corporation integrated circuits. For details of design ofsuch a divider see Approximating the Frequencies of the Musical Scalewith Digital Counter Circuits by Roelif Staplefeldt on Page 478 of Vol.46 of the Journal of the Acoustical Society of America.

Audio amplifier 4 feeding to speaker 5 causes the selected note to besounded. In the present case A 440 is sounded. The amplifier may consistof two cascaded transistors type 2Nl7l 1 made by Texas InstrumentsCorporation coupled as emitter followers.

Microphone 7 picks up the note from the musical instrument being tuned.The resultant signal is amplified by amplifier 8 and fed to sensitivitydivider 9. This signal will be approximately 440 HZ. Amplifier 8 may bean RCA type 3010A integrated circuit. Divider 9 may be a TTL 7493.

Amplifier 8 is overdriven so that the output is essentially a squarewave capable of acting as a suitable digital input to sensitivitydivider 9. Alternatively a Schmitt trigger may be interposed between thetwo items. However, this was found unnecessary.

The output of octave divider 2 is fed to a second programmable divider 6consisting of eight stages. The programming of this divider iscoordinated with the programming of divider 3 so that the frequency ofthe output of divider 6 is approximately 16 times the frequency of theoutput of divider 3. The output of divider 6 feeds to sensitivitydivider 10. Divider 6 is reset by divider 3. Consequently the outputpulse train from divider 6 is repeated once for each output pulse fromdivider 3. Divider 6 may be formed of two cascaded TTL type 8281Aintegrated circuits.

The output selector switches of dividers 9 and 10 are ganged.

Binary to hexadecimal converter 12 is an integrated circuit (TTL type74154) commonly available. It has 16 outputs. Any one of the 16 outputsis selected in accordance with a four bit select code delivered on fourinput lines. However, for any of the output lines to be activated anEnable" signal must also be received.

The select code for converter 12 is provided by the Enable signalsobtained directly from the switch associated with divider 9.

A display 13 consisting of 16 Leds 14 formed in a circle is fed from theoutputs of converter 12. The arrangement is such that only one Led isaddressed at any one time. This Address moves sequentially around thecircle. For the present case of A 440, the movement is at a rate closelyapproximating 440 revolutions per second.

If audio amplifier 8 is overdriven, the Enable signal will be highapproximately 50 percent of the time. If the note sounded into themicrophone is exactly 440 Hz, a stationary pattern of half the Leds litand the other half unlit will appear in display 13. If the note soundedinto microphone 7 is low, the pattern appearing on display 13 willrotate in a first direction. If the note sounded is high, the patternwill rotate in the opposite direction. Rate of rotation will depend uponhow far off the sounded note is from the reference signal. If it is offby 1 hertz, the patternwill rotate once per second. If it is off by Hz,the rotation will approach the flicker rate and the eye will hardly beable to tell in which direction the pattern is rotating.

To reduce the flicker problem, sensitivity dividers 9 and 10 have beenincorporated. They provide for division by factors of 2,4,8, and 16. ifthe selector switch is set to the 16 position, then an error of l6 Hzfor the sounded note will cause a rotation in the display of onerevolution per second. For A 440 the l6 Hz is more than half a semitone.Consequently the sensitivity divider having four binary stages appearsadequate. Integrated circuits used in the divider may be TTL 7493.

ALTERNATE EMBODIMENTS In some cases a band leader may desire to tunehigh by a few cents or perhaps low by a few cents. In these casesoscillator 1 may be replaced or supplemented by variable frequencyoscillator 14. Varying the frequency of this oscillator from theprescribed 8,166,645 Hz causes the entire range of reference frequenciesto move up or down by a proportionate amount. A suitable variablefrequency oscillator using an FET 3Nl28 is described by Hanchett in theOct. 1960 issue of QST.

Alternatively a frequency synthesizer may be used, of which severaltypes are presently reaching that state of development where they can beeconomically applied.

Binary to hexadecimal converter 12 operated in conjunction with selectcode divider 11 may be replaced by a shift register fed directly fromdivider 10. This system is more economical. It has been tried and workswell.

A Schmitt trigger (TTL 7413 made by Texas Instruments Corporation) maybe inserted between amplifier 8 and divider 9. This removes therequirement for overdrive on amplifier 8.

A Schmitt trigger may be inserted ahead of divider 2 in those caseswhere the oscillator does not give a digitally compatible signal.

Alternate embodiments involve different combinations of the sections ofFIG. 1. To cover only one octave, divider 2'may be omitted and thefrequency of oscillator l shifted to provide outputs in the desired 6range. If only reference tones are desired, all circuitry associatedwith the display may be omitted. If only the display is desired, theaudio output circuitry may be omitted.

It is apparent that increasing the frequency of oscillator 1 by a factorof 16 will permit divider 6 to be eliminated. However, anotherdivide-by-l6 divider must be inserted between divider 3 and amplifier 4.The 8 MgI-lz oscillator is near the upper limit of conventional TTLtechnology, which fact precludes use of this technique at present. AsSchottky TTL becomes available or ECL comes into common use, thisapproach will probably prove preferable.

It is also apparent that the display may be in a straight line ratherthan in a circle. Also, the sweep rate need not be closely related tothe reference frequency as is provided presently by dividers 6 and 10.The only requirement is that the sweep be triggered by the output ofdivider 3. An entirely separate system may be used in place of dividers6, l0, and 11. One such system would consist of a simple multivibratorfeeding a shift register, the shift register being reset by the outputof divider 3.

It is also apparent that the sweep of the display need not be at a rateequal to the frequency of the note under consideration. A sweep rate of440 Hz causes one lobe of lit Leds and one lobe of unlit Leds. A sweeprate of 220 Hz causes two lit lobes and two unlit lobes. A sweep rate of147 Hz causes three lit and three unlit lobes. And so on. However, theclearestindication accrues from the one-to-one correspondence infrequencies. The sweep rate may not be higher than the frequency of thetone under consideration.

In another alternate embodiment the input to the output audio amplifier4 is taken from the output of sensitivity divider 10 rather than fromprogrammable divider 3. This is indicated by the dotted line in FIG. 1.The output of divider 10 is essentially a square wave of the samefrequency as the output of divider 3. Output of divider 3 is far from asquare wave for frequencies near the top of the octave. Since a squarewave provides optimum drive for the amplifier, taking the signal fromdivider 10 improves performance.

I claim:

1. A musical tuning instrument comprising:

a reference signal source generating a reference signal of referencefrequency;

an octave divider comprising cascaded binary divider stages forreceiving said reference signal and producing at the output of eachsuccessive stage a signal whose frequency is half the frequency of theinput of said stage and means for selecting the output of a particularstage;

a primary programmable divider consisting of cascaded binary dividerstages for receiving said selected output from said octave divider andadapted for being programmed in twelve modes each successive modeproducing as a final output of said primary programmable divider asignal whose frequency is that of a successive musical note of theparticular octave corresponding to said selected output of said octavedivider;

a secondary programmable divider accepting as input the output of saidoctave divider and similar to said primary programmable divider but.consisting of four fewer stages and adapted to produce at its output asignal whose frequency is approximately 16 times the frequency of saidfinal output of said primary programmable divider, said secondaryprogrammable divider being adapted for being reset by said final outputof said primary programmable divider;

an audio input section consisting of an acoustical pickup feeding to anaudio amplifier and producing a digitally compatible output in responseto an audio input;

an audio input sensitivity divider consisting of cascaded binary stagesthe output of each stage being a signal whose frequency is half thefrequency of the input to said stage and accepting as input the outputof said audio input section;

a reference sensitivity divider consisting of the same number ofcascaded binary stages as said audio input sensitivity divider, theoutput of each stage being a signal whose frequency is half thefrequency of the input to said stage and accepting as its input theoutput of said secondary programmable divider;

means for selecting the output of one of the stages of said audio inputsensitivity divider and simultaneously selecting the output of thecorresponding stage of said reference sensitivity divider;

a display consisting of sixteen light emitting diodes;

and

a drive circuitry having a first input and a second input and adapted tocause each diode in succession to be activated in response to successivehighs of said second input if and only if said first input is highsimultaneously, said first input being the selected output of said audioinput sensitivity divider, and said second input being the selectedoutput of said refrence sensitivity divider.

2. A musical tuning instrument as in claim 1 and having an audio outputsection comprising an audio amplifier and a speaker for receiving theoutput of said primary programmable divider and generating acorresponding tone.

3. A musical tuning instrument as in claim 1 and having an audio outputsection (comprising an audio amplifier and a speaker for receiving anappropriate output of said reference sensitivity divider and generatinga corresponding tone) adapted for receiving the output of an appropriatestage of said reference sensitivity divider and generating an audio toneof like frequency. l l

1. A musical tuning instrument comprising: a reference signal sourcegenerating a reference signal of reference frequency; an octave dividercomprising cascaded binary divider stages for receiving said referencesignal and producing at the output of each successive stage a signalwhose frequency is half the frequency of the input of said stage andmeans for selecting the output of a particular stage; a primaryprogrammable divider consisting of cascaded binary divider stages forreceiving said selected output from said octave divider and adapted forbeing programmed in twelve modes each successive mode producing as afinal output of said primary programmable divider a signal whosefrequency is that of a successive musical note of the particular octavecorresponding to said selected output of said octave divider; asecondary programmable divider accepting as input the output of saidoctave divider and similar to said primary programmable divider butconsisting of four fewer stages and adapted to produce at its output asignal whose frequency is approximately 16 times the frequency of saidfinal output of said primary programmable divider, said secondaryprogrammable divider being adapted for being reset by said final outputof said primary programmable divider; an audio input section consistingof an acoustical pickup feeding to an audio amplifier and producing adigitally compatible output in response to an audio input; an audioinput sensitivity divider consisting of cascaded binary stages theoutput of each stage being a signal whose frequency is half thefrequency of the input to said stage and accepting as input the outputof said audio input section; a reference sensitivity divider consistingof the same number of cascaded binary stages as said audio inputsensitivity divider, the output of each stage being a signal whosefrequency is half the frequency of the input to said stage and acceptingas its input the output of said secondary programmable divider; meansfor selecting the output of one of the stages of said audio inputsensitivity divider and simultaneously selecting the output of thecorresponding stage of said reference sensitivity divider; a displayconsisting of sixteen Light emitting diodes; and a drive circuitryhaving a first input and a second input and adapted to cause each diodein succession to be activated in response to successive highs of saidsecond input if and only if said first input is high simultaneously,said first input being the selected output of said audio inputsensitivity divider, and said second input being the selected output ofsaid refrence sensitivity divider.
 2. A musical tuning instrument as inclaim 1 and having an audio output section comprising an audio amplifierand a speaker for receiving the output of said primary programmabledivider and generating a corresponding tone.
 3. A musical tuninginstrument as in claim 1 and having an audio output section (comprisingan audio amplifier and a speaker for receiving an appropriate output ofsaid reference sensitivity divider and generating a corresponding tone)adapted for receiving the output of an appropriate stage of saidreference sensitivity divider and generating an audio tone of likefrequency.